As a resin having excellent characteristics such as heat resistance, transparency, lightweight property, steam resistance, releasability, gas permeability and electrical property as compared with polyethylene or polypropylene, a 4-methyl-1-pentene (co)polymer is utilized in various fields of food containers, subsidiary materials for electronic information members, experimental instruments, stationeries, process members for bridging, release films, films for electronic information members, food packaging materials, synthetic papers, etc.
The (co)polymer, however, is generally poor in elongation, toughness and stretchability, and in the actual circumstances, therefore, its applicable uses are limited as compared with, for example, polyethylene or polypropylene that is the same polyolefin. Further, the (co)polymer is generally poor in stretchability, and therefore, production of a stretched film from the (co)polymer or blow molding or vacuum forming of the (co)polymer is difficult as compared with polyethylene or polypropylene that is the same polyolefin, so that the region wherein the (co)polymer can be used is limited.
To cope with them, various researches have been attempted for the purpose of improving toughness and elongation of the 4-methyl-1-pentene (co)polymer.
For example, a wrapping film composed of a polymer obtained by copolymerizing 4-methyl-1-pentene and 1-hexene in a specific ratio has been studied in a patent literature 1. In this case, transparency and elongation of the film have been improved, but heat resistance that is a characteristic of a 4-methyl-1-pentene polymer tends to be lowered.
In a patent literature 2, a hose composed of a thermoplastic elastomer containing a 4-methyl-1-pentene-based polymer having excellent elongation and flexibility has been disclosed. This hose tends to be deteriorated in transparency because a crosslinked rubber is present in the composition.
In a patent literature 3 and a patent literature 4, elongation is imparted to a film by laminating polyester or polyamide that is rich in toughness and elongation and a composition containing a 4-methyl-1-pentene polymer to each other. Since multi-ply lamination of non-polar polyolefin and polyester or polyamide that is a polar resin is carried out, occurrence of ply separation is expected. If an adhesive resin is used in combination in order to inhibit it, the molding method and the molding apparatus become complicated, so that increase in production cost is thought to be induced, and there is a fear of lowering of transparency.
In the prior art described above, a copolymer having been controlled in the type of an olefin or the ratio between an olefin and 4-methyl-1-pentene in the copolymerization of 4-methyl-1-pentene and an olefin or a composition of the copolymer and various modifiers is obtained, or toughness and elongation are imparted by laminating the copolymer or the composition to another sheet or film, and therefore, a balance between heat resistance, transparency and mechanical properties which are characteristics of a 4-methyl-1-pentene copolymer cannot be maintained in some cases.
Further, various researches have been attempted in the past for the purpose of improving stretchability of a 4-methyl-1-pentene (co)polymer.
For example, in a patent literature 5, a liquid hydrocarbon compound is added to a 4-methyl-1-pentene-based polymer resin. In this case, a sheet produced sometimes undergoes blocking, or bleed out of the hydrocarbon compound sometimes occurs when the sheet is heated.
In a patent literature 6, a 4-methyl-1-petene-based polymer resin of high fluidity and a 4-methyl-1-pentene-based polymer resin of low fluidity are mixed under the specific conditions. In this case, bad dispersing of the polymer resin of low fluidity takes place, or because fluidity of the mixture is lowered, bad flow such as melt fracture or surging takes place during molding. Moreover, the molding method used is limited because of fluidity.
In a patent literature 7, uniaxial stretchability is imparted to a 4-methyl-1-pentene (co)polymer film by multi-play lamination of the (co)polymer and polyethylene or polypropylene that is easily stretched. In this case, peeling is required after stretching, and it is difficult to obtain a thin and uniform film.
In the prior art described above, in order to impart stretchability to a 4-methyl-1-pentene (co)polymer, a low-molecular weight compound or a high-fluidity resin is added to the (co)polymer in a maximum amount of 30% by weight, as a modifier for improving fluidity of the (co)polymer, or a molding processing method is devised by using multi-ply lamination or the like, but such a means is not intended to improve the effects restricted by the amount added or the molding conditions or to improve stretchability of the resin itself.
As raw materials of resin containers, polyolefins such as polyethylene and polypropylene and polyesters such as polyethylene terephthalate have been mainly used.
For example, polyolefins such as polyethylene and polypropylene are widely used for containers/bottles for liquids, fuel tanks, etc., and such containers, etc. are generally produced by injection molding or blow molding. The molded products, however, are sometimes inferior in transparency (patent literature 8).
On the other hand, polyesters such as polyethylene terephthalate are widely used mainly for beverage containers, and such containers are produced by injection blow molding (sometimes referred to as “injection blowing” hereinafter). In this molding method, a molded product called a preform is prepared by injection molding, and thereafter, the preform is reheated and then subjected to blow molding to prepare a molded product. The molded product, however, has a problem of heat resistance though it is excellent in transparency (patent literature 9).
Here, in order to impart heat resistance to polyethylene terephthalate, an attempt to produce a molded product in a system wherein engineering plastic such as polycarbonate or polyether sulfide is added has been also made, but from the viewpoints of hygienic property due to residual monomers and cost, use of it is limited to only a part of applications (patent literature 10).
In recent years, in order to obtain molded products improved in heat resistance that is a defect of polyethylene terephthalate, various researches regarding injection blow molded products using polypropylene have been made (patent literatures 11 to 13). In the case of polypropylene, however, handling during molding is frequently difficult because the molding temperature range is narrow. In addition, there resides a disadvantage that available polypropylenes (type, properties, etc.) are few. For example, when homopolypropylene is used, transparency is rarely exhibited, or when random polypropylene is used, heat resistance is low.
In order to solve such problems of transparency and heat resistance as above, researches of molded products using 4-methyl-1-pentene-based polymers have been made. However, hitherto known 4-methyl-1-pentene-based polymers that are usually on the market cannot be necessarily said to have good moldability. For example, when a molded product is obtained by blow molding, there is a problem that it is difficult to produce the molded product by the use of a 4-methyl-1-pentene-based polymer because the polymer has low mechanical strength and low melt tension as compared with polyethylene or polypropylene that is the same polyolefin.